论文部分内容阅读
液体中脉冲大电流放电产生强有力的激波被广泛应用于工业生产、生物医疗等领域,如何稳定、高效地获得高强度的激波是该技术的关键.基于搭建的液电脉冲激波实验平台,该文研究了正极性针-板放电模式对激波强度的影响.通过高速摄像机拍摄流注通道发展过程,发现流注可能呈现出两种不同的发展模式:树枝状亚音速流注与丝带状超音速流注.试验结果表明放电电压对水中间隙击穿放电模式及对应的激波强度有明显影响.通过改变放电电压,可以实现对水中间隙击穿放电模式的调控.亚音速流柱的发展过程属于电热击穿过程,阳极尖端首先出现可见的气泡簇,在外部不均匀电场的作用下气泡簇内部明亮流注沿着尖端向阴极发展,形成树枝状的流注通道.此后,气泡簇包裹的丛林状流注通道不断向阴极发展,当流注头部发展到与阴极距离足够小时,水中间隙击穿并产生强烈的激波.超音速流注的出现可导致间隙的快速动态击穿,电容器上的能量可实现快速释放,形成更为强烈的激波.针对本试验条件,充电电压提升到22.5kV时,亚音速流注将向超音速流注转化,预击穿过程的击穿时延及泄漏能量将迅速降低.研究表明超音速流柱模式的能量转换效率更高,即使在相同的施加电压下,超音速流柱对应激波强度可以达到亚音速流柱模式下的2～4倍.“,”Shock waves generated by underwater pulsed discharge have been applied to industrial and bio-medical treatments,and the key technology is to induce powerful shock waves steadily and efficiently.Based on the underwater pulsed discharge platform,the effect of the electrical breakdown discharge modes on the shock wave intensity in water is discussed in the pin-to-plate configuration.Based on the analysis of discharge images captured by a high-speed camera,it can be concluded that the discharge modes are classified as subsonic bush-like streamers or supersonic filamentary streamers.Experimental results demonstrate that the amplitude of applied voltage has a great influence on the discharge modes as well as the shock wave intensity.The mechanism of the subsonic streamer in lower applied voltage is more likely a electrothermal process.The microbubbles are firstly generated and then discharge occurs in the bubble cluster.The volume of bubbles grows until a breakdown of the underwater gap,and the shock wave is generated.The time delay of the subsonic streamer is within hundreds of μs.In higher applied voltage,the energy loss in the pre-breakdown process are reduced significantly as well.In the experimental conditions a threshold value of 22.5kV is necessary for the subsonic streamers turning into supersonic streamers.The electrical breakdown discharge modes can be controlled by changing the applied voltage,and the intensity of the shock wave differs 2～4 times in different discharge modes even in the same applied voltage.